The present invention relates generally to rotary electric switches and, more particularly, to rotary electric switches having a momentary switch position.
Rotary electric switches are well-known in the art and are commonly used to control alternating current circuits for a variety of applications. For example, rotary electric switches are particularly useful in connection with multispeed electric motors for household appliances, such as food processors, blenders, fans and the like.
One type of rotary electric switch which is well-known in the art includes a hollow housing which is preferably miniature in size. The housing is usually made of plastic and includes a recessed base and a cover member. A rotatable contactor is centered in the base and is controlled by a switch handle or shaft. A plurality of resilient stationary contacts are positioned edgewise in the base around the rotatable contactor for making and breaking the several circuits through the switch.
Each stationary contact is generally in the shape of a Z, where the ends of the Z represent a locking tongue and a spring contact finger which are joined together by an intermediate arm. The two bends in the Z shaped stationary contact, one where the locking tongue engages the intermediate arm and the other where the intermediate arm engages the contact finger, are supported in opposite pockets in the base so that the intermediate arm will flex slightly to distribute the bending stresses exerted on both the locking tongue and the spring finger.
The locking tongue on each stationary contact provides the switch with the capability of implementing push-in wire terminals. In particular, a wire to be connected to the switch is pushed through a wire receiving opening formed in the base, the wire receiving opening being partially covered by the free end of the locking tongue of the stationary contact. Once forced through the wire receiving opening, the wire will displace the locking tongue away from the opening which enables the wire to be fed into the base. Once the wire is sufficiently pushed through the opening, the locking tongue engages the side of the wire and effectively locks the wire within the switch between the stationary contact and a sidewall of the housing. When a pulling force is exerted to remove the wire from the switch, the wire tends to carry the tongue with it so that the locking tongue is pushed harder against the wire wedging it against the side wall of the plastic housing, the force of the wedging pressure increasing in proportion to the pulling force exerted on the wire.
U.S. Pat. No. 5,750,947 to C. P. Rao et al discloses a rotary electric switch having push-in wire terminals. The rotary electric switch includes a hollow plastic housing having a recessed base and a cover, the base having a plurality of wire receiving openings. A plurality of resilient stationary contacts are positioned in the base, each resilient stationary contact being generally Z-shaped and having a locking tongue at one end, an intermediate arm, and a spring finger at the opposite end from the locking tongue. Each resilient stationary contact is positioned in the base with its locking tongue overlying a wire receiving opening in a side wall in the housing. A rotatable contactor is mounted in the base between the spring fingers of the resilient stationary contacts. A plurality of conductive plates are disposed in the base, one conductive plate associated with each resilient stationary contact, each conductive plate contacting the resilient stationary contact at a location its intermediate arm and in addition preventing a wire inserted into the opening from touching the sidewall of the housing. The housing includes a number of projections and standoffs to provide adequate spacing between current carrying components on the switch.
The use of rotary electric switches with push-in wire terminals is desirable for two primary reasons. First, connecting the wires of the circuit into the switch is relatively simple. More specifically, the user simply inserts each wire through its associated wire receiving opening in the housing, the locking tongue serving to lock the wire within the switch and to preclude its removal. Second, the use of push-in wire terminals is relatively inexpensive when compared to the more complicated switches which are presently quite standard in rotary switches, such as spade terminals.
Rotary electric switches of the type described above are typically constructed to include multiple stationary switch positions. Stationary switch positions, also commonly referred to as snap-action contact positions or stable state positions, refer to the switch positions, or settings, which are assumed by the switch upon rotation of the switch handle and which remain in the particular position even after the rotative force has been removed from the switch handle. More specifically, for rotary electric switches of the type described above, the switch handle is engageable with the rotatable contactor and includes detent notches along its periphery which are engageable with the spring contact finger of the stationary contacts in order to lock the position of the switch handle in place.
Rotary electric switches having multiple stationary switch positions are well-known and are widely used in commerce. However, for many applications, especially those involving electric food mixers, it is frequently desirable to be able to produce an abrupt increase of power at a predetermined selected speed for a limited time period and then to release, or desist from, the predetermined speed of operation almost instantaneously. Accordingly, electric switches having momentary switch positions are well known in the art and are commonly used to produce a particular pulse of power which will instantaneously terminate upon release of the switching force by the user.
As can be appreciated, rotary electric switches having push-in wire terminals are often constructed to provide a momentary switch setting in addition to the multiple stationary positions. Specifically, a coiled wire, or spring, is often disposed between the switch handle and the base of the housing. One of the plurality of stationary contacts is removed from the base of the switch and the coiled wire is disposed within the region of the base in which the removed contact was previously disposed. Accordingly, the application of a rotative force on the switch handle to the momentary switch position causes the wire to wind up in torsion and engage a portion of the base of the housing. Because the coiled wire is wound up in torsion through rotation of the switch handle, upon release of the rotative force, the wound-up wire biases the switch handle away from the momentary switch position.
Rotary electric switches having a momentary switch position of the type described above often experience numerous disadvantages.
As a first disadvantage, it has been found that rotary electric switches of the type described above require that one stationary contact be removed from the switch in order to provide a region of the recessed base in which the coiled wire can be disposed to accommodate the momentary switch position. As a result, the switch is deprived of a stationary switch position.
As a second disadvantage, it has been found that rotary electric switches of the type described above are difficult to manufacture. Specifically, because a coiled wire is disposed between the rotor and the recessed base, the assembly process becomes increasingly complicated. In particular, it has been found that, during assembly, the coiled wire often becomes tangled with the stationary contacts disposed on the recessed base.
As a third disadvantage, it has been found that rotary electric switches of the type described above are unreliable. Specifically,. because a coiled wire is disposed between the rotor and the recessed base, the rotor is often thinned-out in thickness to accommodate the coil. As a result, the rotor is weakened and is susceptible to failure.
As a fourth disadvantage, it has been found that rotary electric switches of the type described above are difficult to use. Specifically, because the coiled wire must be wound up in torsion in order to experience the momentary switch setting, the user is required to expend a significant amount of energy to load the wire.